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Interest Calculator

Calculate simple or compound interest with contributions

Investment Details

$
%
Years
Months

Regular Contributions (Optional)

$
$

Tax & Inflation (Optional)

%
%
Ending Balance
$0.00
Total Contributions
$0.00
Total Interest
$0.00

Investment Breakdown

100.0%
Initial Investment
$10,000.00
Interest Earned
$0.00
Effective Rate
0% per year
Total Return
0%

Investment Growth

Understanding Interest Calculations

Simple Interest vs Compound Interest

Simple Interest

Simple interest is calculated only on the principal amount. The formula is:

Interest = Principal × Rate × Time

Example: $1,000 at 5% for 3 years = $1,000 × 0.05 × 3 = $150 interest

Compound Interest

Compound interest is calculated on the principal plus accumulated interest. The formula is:

A = P(1 + r/n)^(nt)
  • • A = Final amount
  • • P = Principal
  • • r = Annual rate (decimal)
  • • n = Compounds per year
  • • t = Time in years

Compounding Frequency Impact

The frequency of compounding significantly affects your returns. More frequent compounding leads to higher returns due to interest earning interest more often.

Daily (365x)Highest returns
Monthly (12x)Common for savings
Quarterly (4x)Typical for bonds
Annually (1x)Simplest calculation

Regular Contributions

Adding regular contributions dramatically increases your investment growth through:

  • •Dollar-cost averaging: Reduce impact of market volatility
  • •Compound growth: Each contribution starts earning interest
  • •Timing matters: Contributing at the beginning of periods yields more interest

Tax & Inflation Considerations

Tax Impact

Interest earnings are typically taxable. The calculator shows your after-tax returns based on your tax rate. Consider tax-advantaged accounts like IRAs or 401(k)s for retirement savings.

Inflation Adjustment

Inflation reduces purchasing power over time. A 3% inflation rate means prices double approximately every 24 years. The inflation-adjusted value shows what your investment will be worth in today's dollars.

Investment Tips

  • • Start early - time is your greatest asset for compound growth
  • • Be consistent with contributions, even small amounts matter
  • • Choose appropriate compounding frequency for your goals
  • • Consider tax-advantaged accounts for long-term savings
  • • Factor in inflation when planning for future needs
  • • Diversify investments to manage risk